The current (2bfe01e) torvalds git tree fails to build with the following error arch/powerpc/kernel/time.c: In function ‘running_clock’: arch/powerpc/kernel/time.c:712:25: error: implicit declaration of function ‘cputime_to_nsecs’ [-Werror=implicit-function-declaration] return local_clock() - cputime_to_nsecs(kcpustat_this_cpu->cpustat[CPUTIME_STEAL]); ^ I would like to do more than just file a bug report. Further investigation (cputime.h) shows that cputime_to_nsecs has a preprocessor guard on the config option (currently enabled) CONFIG_VIRT_CPU_ACCOUNTING_NATIVE. CONFIG_PPC_PSERIES is also enabled. The offending code in arch/powerpc/kernel/time.c is #ifdef CONFIG_PPC_PSERIES /* * Running clock - attempts to give a view of time passing for a virtualised * kernels. * Uses the VTB register if available otherwise a next best guess. */ unsigned long long running_clock(void) { /* * Don't read the VTB as a host since KVM does not switch in host * timebase into the VTB when it takes a guest off the CPU, reading the * VTB would result in reading 'last switched out' guest VTB. * * Host kernels are often compiled with CONFIG_PPC_PSERIES checked, it * would be unsafe to rely only on the #ifdef above. */ if (firmware_has_feature(FW_FEATURE_LPAR) && cpu_has_feature(CPU_FTR_ARCH_207S)) return mulhdu(get_vtb() - boot_tb, tb_to_ns_scale) << tb_to_ns_shift; /* * This is a next best approximation without a VTB. * On a host which is running bare metal there should never be any stolen * time and on a host which doesn't do any virtualisation TB *should* equal * VTB so it makes no difference anyway. */ return local_clock() - cputime_to_nsecs(kcpustat_this_cpu->cpustat[CPUTIME_STEAL]); } #endif Can anyone give me a hint on this one? Where to start reading? thanks, Tobin.